JPH0677244B2 - Disk cache device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disk cache device, and more particularly to a disk access detection method for realizing a sequential access detection method and a prefetch execution timing upon sequential access detection. It is a thing.

[Conventional technology]

The prefetch method improves the hit rate of the cache memory by predicting the access of the central processing unit and storing the data in the cache memory before the actual access from the central processing unit. Since the disk cache device and the magnetic disk device cannot be accessed from the central processing unit during the pre-fetching process during use, it is desirable to perform the pre-fetching process efficiently in a short time.

In particular, as a pre-fetch method that extends between tracks when it is predicted that the access from the central processing unit is sequential access, I) the records in the tracks are sequentially accessed, and when the last record of the tracks is accessed, the next track is accessed. Pre-fetching method.

II) When a certain track is accessed, if it is a "miss", the previous track is investigated, and the records in the track are accessed sequentially, and if the last record of the track is accessed, the accessed track is accessed. A method of pre-fetching the next track.

Etc.

[Problems to be solved by the invention]

In the case of the above method I, if the central processing unit is processing a plurality of files in a time-sharing manner, the head of the magnetic disk moves to another cylinder before the final record processed by the cache unit is accessed. Then, there is a problem that a seek operation is required to perform pre-fetching, and there is a problem of overhead.In the case of method II, access to the track stored on the cache by pre-fetching is a cache hit, so that The next track had the problem that it was not prefetched.

[Means for solving problems]

The disk cache device of the present invention controls a magnetic disk device having a large number of cylinders, a plurality of tracks in each cylinder, and a plurality of records in each track, and stores a data slot for storing all records in one track. In a magnetic disk subsystem having a cache memory having a large number of cache memory, means for recording a flag indicating that all the records of the tracks of the magnetic disk device have been stored in the data slot for each data slot, and central processing for each data slot. A counter for determining the continuity of records accessed by the device and a record number field for recording the record number last accessed by the central processing unit are provided, and the counter is provided when the central processing unit accesses a predetermined record. If is “0”, the counter is Record the accessed record number in the record number field, and if the counter is 1 or more, check the continuity between the accessed record number and the record number recorded in the record number field. If it is continuous, the counter is incremented by "1" and the accessed record number is recorded in the record number field, and if it is discontinuous, the counter is set to "0", and the central processing unit stores the data. When the last record of the track in the slot is accessed and the input / output operation is terminated, if the above counter is N (N: an integer of 1 or more) or more, the track next to the accessed track is the prefetch target track, If this prefetch target track does not exist in the cache memory, its Secures a data slot for the prefetch target track on the memory and investigates whether the head of the magnetic disk device is positioned in the cylinder containing the prefetch target track. If it is positioned, all of the prefetch target tracks are located in the data slot. Means for storing the record of "0" in the record number field of the data slot, and an integer of N or more in the counter when not positioned, and the head of the magnetic disk device includes the prefetch target track by the above investigation. When the central processing unit accesses the record that was not stored in the data slot for the prefetch target track because it was not positioned in the cylinder, and completed the input / output operation, all the records of the prefetch target track were recorded. If the counter is equal to or more than N after the processing of storing in the data slot, the track next to the accessed track is set as the prefetch target track, and if this prefetch target track does not exist in the cache memory, the cache memory After securing the data slot for the prefetch target track above, investigate whether the head of the magnetic disk device is positioned in the cylinder including the prefetch target track, and if it is positioned, all of the prefetch target tracks in the data slot. Stores the record, and if it is not located, “0” in the record number field of the data slot,
And a means for recording an integer of N or more in the counter.

[Action]

In the present invention, sequential access detection and prefetching are performed while minimizing the overhead of the disk cache device.

〔Example〕

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

In the figure, 1 is a disk cache device, and this disk cache device 1 is a microprocessor 2 and a cache adapter 3 and a cache memory 4 and a host adapter 5 having a large number of data slots for storing all the records in one track. It comprises a disk interface adapter 6. A host processor (central processing unit) 7 is provided as a host device, and this host processor 7 is connected to the host adapter 5.
Further, magnetic disk devices 8 ₁ , 8 ₂ and 8 ₃ each having a large number of cylinders, a plurality of tracks in each cylinder, and a plurality of records in each track are connected to the disk interface adapter 6.

Then, the microprocessor 2, the cache memory 4, and the magnetic disk devices 8 ₁ to 8 ₃ are flags for displaying, for each data slot, that all the records of the tracks of the magnetic disk devices 8 ₁ to 8 ₃ have been stored in the data slot. It constitutes a means for recording.

Further, the microprocessor 2, the cache memory 4 and the host processor 7 store a counter for determining the continuity of the record accessed by the central processing unit for each data slot and the record number last accessed by the central processing unit. Provide a record number field to record,
If the counter is "0" when the central processing unit accesses a predetermined record, the counter is set to "1" and the accessed record number is recorded in the record number field, and the counter is "1" or more. If so, the continuity of the record number accessed and the record number recorded in the record number field is checked, and if it is continuous, the counter is incremented by "1" and the accessed record number is recorded in the record number field. If it is discontinuous, a means for setting the counter to "0" is configured.

Also, the microprocessor 2, the cache memory 4, the host processor 7, and the magnetic disk devices 8 ₁ to 8 ₃
Is the next track of the accessed track if the counter is N or more (an integer of 1 or more) when the central processing unit accesses the last record of the track in the data slot and finishes the input / output operation. If the target track for prefetching and the track for prefetching are not present in the cache memory 4, the data slot for the target track for prefetching is secured in the cache memory 4 and the heads of the magnetic disk devices 8 ₁ to 8 ₃ are secured. Is checked in the cylinder containing the pre-fetch target track, and if it is, all the records of the pre-fetch target track are stored in the data slot. If it is not, the record number field of the data slot is "0", A means to record an integer of N or more in the counter I am configuring.

The operation of the embodiment shown in FIG. 1 will be described below with reference to FIGS. FIG. 2 and FIG. 3 are explanatory views of records on the magnetic disk device and explanatory tables of tables used in the present invention for explaining the operation of FIG.

Fig. 2 is an image of the tracks on the magnetic disk devices 8 ₁ to 8 ₃ , where TR _{1 to} TR ₃ show consecutive tracks in the same cylinder of a certain magnetic disk device, and R ₁₁ , R ₁₂ ... R ₃₄ are The records recorded in the respective tracks TR _{1 to} TR ₃ are shown.

The memory capacity of the cache memory 4 is considerably smaller than the recording capacity of the magnetic disk devices 8 ₁ to 8 ₃ subordinate to the disk cache device 1, and the memory capacity of the cache memory 4 is equal to that of the magnetic disk devices 8 ₁ to 8 ₃ . Since it is not possible to store all of the above data, the data to be stored in the cache memory 4 is selected by the LRU algorithm or the like. The cache memory 4 is a semiconductor memory having a continuous address space, and Y data buffers are logically allocated in the cache memory 4.

Figure 3 is an image of this the data buffer, the data storage area 34, data for one track portion of the magnetic disk device 8 _{1-8 3} are stored. Incidentally, 31 indicates a flag, 32 indicates a counter, and 33 indicates a record number.

Although not shown in the figure, the cache memory 4 stores directory information for associating the tracks on the magnetic disk devices 8 ₁ to 8 ₃ with the data buffer. The microprocessor 2 refers to this directory information. By doing so, it is possible to know whether the data buffer is assigned (hit) or not (miss) to a certain track. In addition, the microprocessor 2 operates this directory information to
It is possible to deallocate an appropriate data buffer, and to allocate the releasing data buffer to another track.

When the host processor 7 requests read access to a certain record, the microprocessor 2
Makes a hit / miss decision by referring to the directory information. And, when there is a mistake, the microprocessor 2 is LRU
An appropriate data slot is selected by an algorithm and released from the allocation, and the released data slot is allocated to the track including the accessed record. At this time, the microprocessor 2 sets the flag in the data slot.
31, counter 32, record number 33 (see Fig. 3) are initialized to "0".

After that, the microprocessor 2 locates the heads of the magnetic disk devices 8 ₁ to 8 _{3 on} the target track, reads the target record from the magnetic disk devices 8 ₁ to 8 ₃ and sends it to the host processor 7 and at the same time the data slot. In addition, after the input / output operation of the host processor 7 is completed, the read operation from the magnetic disk devices 8 ₁ to 8 ₃ is continued until all the records on the track are stored in the data slot. A staging process for setting "1" to the flag 31 shown in FIG. Then, at the time of hit, the microprocessor 2 causes the flag 31 of the corresponding data slot.
Is checked, the target record in the data slot is sent to the host processor 7, and if it is "0", the staging process is performed.

Also, the microprocessor 2 is the host processor 7,
Each time a certain record is accessed, the record number 33 shown in FIG. 3 is updated to the accessed record number. If the counter 32 is "0", this is set to "1", and the record number 33 before the update is set to "1". "And the record number after update
If 33 match, increment the counter 32 by "1",
If they do not match, the counter 32 is set to "0".

This process, for example, the first access is "Miss" Der connexion from the host pro-broken 7, record R ₁₁ shown in FIG. 2, R _12, when accessed in the order of R _13, records R ₁₃
At the end of the access, the counter 32 shown in FIG. 3 becomes counter 32 = “3”, and when the records R ₁₁ , R ₁₂ , R ₁₃ are accessed in this order, the counter 32 = “0” at the end of the access of the record R _12. The order of the access from the host processor 7 can be determined by the value of the counter 32. In this embodiment, the counter 32 is "3".
The above cases are determined to be sequential access.

Then, when the host processor 7 finishes the input / output operation after the host processor 7 accesses the final record (R ₁₄ ) of the track TR ₁ shown in FIG. 2, the microprocessor 2 sets the counter 32 shown in FIG. 3 to "3". if more determines Hitsuto / miss track TR ₂ the track TR ₂ is the next track of the track TR ₁ as Purifuetsuchi target track. Truck T
If R ₂ is a hit, the track TR ₂ has been accessed before this input / output operation, so no operation is performed on the data slot of the track TR ₂ . If the track TR ₂ is miss, the possibility that the track TR ₂ will be accessed in the next input / output operation is further increased. Then, the microprocessor 2 prepares the data slot of the track TR ₂ , and sets "0" to the flag 31 and the record number 33 shown in FIG.
The counter 32 is set to "3". Next, the head positions of the magnetic disk devices 8 ₁ to 8 ₃ are investigated to determine whether or not seek operation is necessary.

When the host processor 7 accesses a plurality of files in a time division manner, the heads of the magnetic disk devices 8 ₁ to 8 ₃ are recorded by the disk cache device 1 as records R ₁₂ , R ₁₃ and R shown in FIG. _While processing ₁₄ on the cache memory 4, it may be moved to a cylinder other than the cylinder containing the track TR ₁ .

When the seek operation is unnecessary, the microprocessor 2 immediately transfers all the records of the track TR ₂ shown in FIG. ₂ to the track TR ₂
And the flag 31 shown in FIG. 3 is set to "1". As a result, when the record R ₂₁ shown in FIG. 2 is accessed as expected in the near conventional input / output operation, a cache hit occurs, and the record number (= “0”) + “1” before update and the record number after update Record number (=
Since "1") is equal, the counter 32 is incremented by "1", and the counter 32 that monitors the order of access still indicates that the input / output operation is sequential access.

If the microprocessor 2 needs a seek operation to pre-fetch the pre-fetch target track,
No prefetching is performed to avoid overhead, but the data slot of track TR ₂ shown in FIG. ₂ is left in the above-mentioned state. Then, when the central processing unit 7 accesses the record R ₂₁ in an input / output operation in the near future, it is a cache hit, but the flag 31 shown in FIG. 3 indicates that the record is not stored. Setsusa 2 is positioned head of the magnetic disk device 8 _{1-8 3} tracks TR _2, the magnetic disk device 8 _1-8
The target record is read from ₃ and the host processor 7
To the magnetic disk devices 8 ₁ to 8 ₃ until all the records on the track are stored in the data slot after the input / output operation of the host processor 7 is completed. Continue and flag
A staging process of setting "1" to 31 is performed. At the end of this staging process, it is determined whether the track TR ₃ shown in FIG. 2 is a pre-fetch target track or not based on the value of the counter 32 shown in FIG. If the track is a pre-targeted track, the seek operation is not required except for the case of straddling the cylinder or after the defective / alternate automatic link operation, so that the pre-fetch is immediately performed.

〔The invention's effect〕

As described above, according to the present invention, sequential access can be detected and prefetching can be executed while minimizing the overhead of the disk cache device, and therefore the performance of the disk cache device can be improved. There is an effect that can be done.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention, and FIGS. 2 and 3 are explanatory diagrams of a record on a magnetic disk device used for explanation of the operation of FIG. 1 and the present invention. It is an explanatory view of a table used in. 1 ... Disk cache device, 2 ... Microprocessor, 3 ... Cache adapter, 4 ... Cache memory, 5 ... Host adapter, 6 ... Disk interface adapter, 7 ... Host processor ( Central processing unit), 8 ₁ to 8 ₃ ... Magnetic disk unit.

Claims (1)

[Claims] 1. A magnetic disk device having a large number of cylinders, a plurality of tracks on each cylinder, and a plurality of records on each track, and a large number of data slots for storing all the records in one track. In a magnetic disk subsystem provided with a cache memory, means for recording a flag indicating that all the records of the tracks of the magnetic disk device have been stored in the data slot for each data slot, and a central processing unit for each data slot. Is provided with a counter for determining the continuity of records accessed by the central processing unit and a record number field for recording the record number last accessed by the central processing unit, and the counter is set when the central processing unit accesses a predetermined record. If it is "0", the counter is set to "1" and the access The recorded record number is recorded in the record number field, and if the counter is "1" or more, the continuity between the accessed record number and the record number recorded in the record number field is checked, and if it is continuous, the counter is recorded. Is incremented by "1" and the accessed record number is recorded in the record number field, and the counter is set to "0" if the record number field is discontinuous, and the central processing unit is the last of the tracks in the data slot. When the record is accessed and the input / output operation is completed, if the counter is N (N: an integer of 1 or more) or more, the track next to the accessed track is set as the prefetch target track, and this prefetch target track is set as the prefetch target track. If it does not exist in the cache memory, the prefetch target After confirming whether the head of the magnetic disk device is positioned in the cylinder containing the prefetch target track after securing the data slot for the recording, if it is, store all the records of the prefetch target track in the data slot. If it is not positioned, "0" is recorded in the record number field of the data slot, means for recording an integer of N or more in the counter, and the head of the magnetic disk device is positioned in the cylinder containing the track to be prefetched by the investigation. When the central processing unit accesses a record that has not been stored in the data slot for the prefetch target track and ends the input / output operation, all the records of the prefetch target track are stored in the data slot. Perform processing Thereafter, if the counter is N or more, the track next to the accessed track is set as a prefetch target track, and if the prefetch target track does not exist in the cache memory, the data for the prefetch target track is stored in the cache memory. It is investigated whether the head of the magnetic disk device is positioned in the cylinder containing the prefetch target track after securing the slot, and if it is positioned, all the records of the prefetch target track are stored in the data slot and the head is positioned. The disk cache device further comprises means for recording "0" in the record number field of the data slot and an integer of N or more in the counter if there is not.